Infinitival clause

Hi,

I would like to know how native speakers distinguish catenative complements from infinitival clauses functioning as adjunct of purpose.

ex1) She was waiting to use the photocopier.

In my grammar book, it says that the sentence can be understood as a catenative construction, but at the same time it can be viewed as adjunct of purpose.

In what context, would it be more appropriate to interprete it as a catenative complement than to interprete it as purpose of adjunct or vice versa?

ex2)

A: She was strong to withstand this pressure.

B: She had the strength to withstand this pressure.

The infinitival in A is an adjunct whereas it is a complement in B.

It's hard for me to understand why the infinitival in A is construed as an adjunct.

In order to withstand this pressure, she was strong.(??)

Could someone shed some light on how to make a clear distincion between the two?

Thanks very much in advance for your help.